Abstract
What would happen in Mediterranean rivers and streams if warming but not drying occurred? We examined whether the delivery of environmental flows within a warming climate can maintain suitable macroinvertebrate habitats despite warming. A two-dimensional ecohydraulic model was used to (1) simulate the influence of water temperature and flow on macroinvertebrates by calculating habitat suitability for 12 climate change scenarios and (2) identify the mechanism by which macroinvertebrate assemblages respond to warming. The results suggest that not all watersheds will be equally influenced by warming. The impact of warming depends on the habitat conditions before warming occurs. Watersheds can, thus, be categorized as losing (those in which warming will degrade current optimal thermal habitat conditions) and winning ones (those in which warming will optimize current sub-optimal thermal habitat conditions, until a given thermal limit). Our models indicate that in losing watersheds, the delivery of environmental flows can maintain suitable habitats (and, thus, healthy macroinvertebrate assemblages) for up to 1.8–2.5 °C of warming. In winning watersheds, environmental flows can maintain suitable habitats when thermal conditions are optimal. Environmental flows could, thus, be used as a proactive strategy/tool to mitigate the ecological impacts of warming before more expensive reactive measures within a changing climate become necessary.
Highlights
Since the 1940s, and mostly since the 1980s, the Earth’s natural cooling–warming cycle has been interrupted by specific, rapidly expanding human activities, outcompeting natural processes
To clarify and further elaborate, we know that in Mediterranean climates, global warming has and will further cause local drying, forcing aquatic ecosystems to eventually adapt [7,8]; but what would happen if rivers kept flowing despite the increased water temperatures? We suggest that if macroinvertebrate habitats remained healthy and able to sustain healthy macroinvertebrate communities, it would be worth researching and funding proactive practices/strategies of delivering environmental flows to rivers to keep their ecosystem habitats healthy and maintain the valuable services they provide to societies, despite the inevitable warming
For discharges up to 50–75% decreased from the current average, water temperature is the major determinant of macroinvertebrate habitat suitability
Summary
Since the 1940s, and mostly since the 1980s, the Earth’s natural cooling–warming cycle has been interrupted by specific, rapidly expanding human activities, outcompeting natural processes. Agro-industrial and residential carbon dioxide (CO2) and methane (CH4) emissions have been strongly associated with a post-1980 steep increase in the global average air temperature [1,2] This global temperature rise—expected to increase by 3–5 ◦C by 2100, compared to the early 2000s [2]—has already caused, and it is expected to intensify, a global climate change that has resulted, inter alia, in more frequent and extreme local floods and droughts [3]. River flows in northern Europe, northern Asia and high-latitude North America are projected to increase by 10–40% by 2050, but in southern Africa, southern Europe, the Middle East and mid-latitude western North America, they are expected to decline by 10–30% [4] These warming-induced hydroclimatic changes have already changed the structure and functioning of Mediterranean freshwater ecosystems, but ecosystem response to climate change varies across regions [9]. There are (and will further be) winners and losers across regions within continents, and across watersheds within regions, both from a hydrological (discharge may increase in some regions (winners) and decrease in others (losers)) and from an ecological perspective (density, biodiversity and richness may increase in some regions (winners) and decrease in others (losers))
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